In general, a nitride semiconductor, which has the characteristics of emitting light within a wide range including the ultraviolet region as well as overall visible wavelength region, has come to prominence as a material used to fabricate a light emitting diode (LED) or a laser diode (LD) emitting visible light, a ultraviolet LED, and a bluish green optical device.
In order to fabricate optical devices including a nitride semiconductor, a technique of growing a nitride semiconductor as a high quality single-crystal thin film is essential. However, with the currently used growth methods, it is difficult to directly grow a high quality nitride semiconductor single crystal due to a lattice mismatch, a mismatch in coefficients of thermal expansion with respect to a growth substrate and limitations in growth conditions, and a plurality of dislocation defects may be generated.
Dislocation may propagate in a growth direction, and in particular, in a semiconductor light emitting device, dislocation proceeds through an active layer, causing degradation of device characteristics.